1. Field of the Invention
This invention relates to air cushion vehicles involving skirted types and side wall types which obtain lift and propulsion from the same engine with the amount of lift being automatically controlled.
2. Description of the Prior Art.
An ordinary air cushion vehicle uses two engines to get proper control. One engine runs the lift fan independent from the other engine which runs the thrust fan. Both engines must be operating for the vehicle to perform properly. Therefore, this vehicle is less reliable than a single engine vehicle. The vehicle operator must manipulate two throttle levers to adjust lift and thrust to meet the requirements of changing conditions. The single engine vehicle uses only one throttle lever. The single engine vehicle is also quieter, lighter in weight and more economical on fuel than the twin.
A single engine hovercraft operating without the automatic lift system of this invention encounters problems and limitations in the course of operation. This type vehicle is generally set up so that at a cruise power setting the lift fan is turning at optimum or design speed. Upon application of full power, the lift fan is being driven at much higher speed than required. In the case of a high-performance vehicle, the lift fan would absorb much of the power which should go to the propulsion fan. Slowing this vehicle after a high-speed run will result in a lack of lift air to maintain the cushion and plowing in at speed. My present invention will maintain proper lift at any throttle position above idle.
Running a hovercraft into a headwind requires extra power for propulsion. The ordinary single engine hovercraft would have to develop too much lift for this case. Running downwind, the ordinary single engine hovercraft would plow in as a result of a lack of lift due to low propulsion requirements. The present invention overcomes this by maintaining essentially the same lift upwind or downwind.
The single engine hovercraft with a controllable pitch propeller is an improvement over the ordinary single engine hovercraft, but it too generally has two control levers; one for throttle control and the other for pitch control. On this type craft the engine must be running relatively fast to maintain lift even though very little propulsion is desired. On the present invention, the engine may be run slow when full lift and very little propulsion is desired. This is due to the drive ratios of the automatic lift system as will be explained later.
The single engine hovercraft of this invention is less expensive to build than a twin engine vehicle because the cost of the automatic lift unit is less than that of a lift engine. Noise is also decreased by elimination of the lift engine because lift engines for small vehicles are usually two-cycle air cooled engines which are known to be noisy. The need for two different types of fuel (two cycle and four cycle) is also eliminated.